RAMAN-STUDY OF HGBA2CAN-1CUNO2N+2+DELTA (N=1,2,3,4 AND 5) SUPERCONDUCTORS

Polarized micro-Raman scattering measurements have been performed on t he five members of the HgBa2Can-1CunO2n+2+delta (n = 1, 2, 3, 4 and 5) high-T-c superconductor family using different laser frequencies. Loc al laser annealing measurements were carried out to investigate the va riation of the Raman spectra with the excess oxygen content, delta. A systematic evolution of the spectra, which display mainly peaks near 5 90, 570, 540 and 470 cm(-1), with increasing number of CuO2 layers has been observed; its origin has been shown to lie in the variation of t he interstitial oxygen content. In addition to confirming that the 590 cm(-1) mode represents vibration of apical oxygens in the absence of neighboring excess oxygen, the 570 cm(-1) mode, which may be composed of some finer structures, has been assigned to the vibration of the ap ical oxygen modified by the presence of the neighboring excess oxygens . The 540 and 470 cm(-1) modes may represent the direct vibration of e xcess oxygens. The implication of possible different distribution site s of excess oxygens is discussed. All other observed lower-frequency m odes are also assigned.